Phase-field Model of Electromechanical and Optical Properties of Ferroelectric Domain Structures

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NONTECHNICAL SUMMARYThis award supports theoretical and computational research, and education to develop computational models and tools for studying piezoelectricity and light transparency of ferroelectric crystals. The piezoelectricity of a material characterizes the ability of the material to generate an electric voltage difference when it is subject to a mechanical stress or to generate a mechanical motion when the materials is subjected to an electric voltage difference or electric field. Light transparency of a solid measures the fraction of the incident visible light transmitted through the material, and it is limited by the amount of light reflection and scattering on the outside surfaces as well as the internal interfaces and the light adsorption inside the solid. Ferroelectrics are materials that contain high density of electric dipoles or polarization in the absence of an applied electric field, and they are the major class of piezoelectric materials exhibiting high piezoelectricity. However, the ferroelectric crystals that possess the highest piezoelectricity tend to be those containing many spatial regions of uniform electric polarization with different polarization directions separated by so-called ferroelectric domain walls. Most of these domain walls scatter and reflect light, and thus even single crystal ferroelectric materials are not completely transparent or tend to be opaque at best. The PI will develop computational models and tools to study both piezoelectricity and light transparency of ferroelectric crystals. The models and tools will be employed to find the optimal combination of optical transparency and piezoelectricity through understanding the roles of the ferroelectric domain wall orientations and domain wall density. Transparent ferroelectric crystals with high piezoelectricity have potential applications in high-throughput photoacoustic biomedical imaging, transparent actuators, self-energy-harvesting touch screens, and invisible robotic devices. The project will train graduate students to become experts in the areas of computational materials science, physics of piezoelectricity, and light propagation in inhomogeneous solids. Graduate students will also be trained in mentoring by co-supervising the research of undergraduate students in materials science and engineering or physics in the PI’s group.TECHNICAL SUMMARYThis award supports theoretical and computational research, and education with the main goal to fundamentally understand the science underlying the roles of domain structures in both piezoelectricity and light transparency of ferroelectric crystals. The award will support the development of a phase-field model of ferroelectric domains and piezoelectricity in both multidomain single crystals and polycrystalline ceramics in the presence of electronic and ionic defects and a spectral method in space with frequency-domain description in time for solving the Maxwell equations of light propagation and obtaining the light transmission spectrum for arbitrary ferroelectric domain structures. The PI and his graduate students will use the computational tools to study the evolution of domain walls, piezoelectricity, electronic charge carriers, and the light transparency at different frequencies under different ferroelectric polarization poling protocols. The developed computational framework and advance in fundamental understanding will then be harnessed to guide the design of ferroelectric domain structures to achieve desired electromechanical and optical properties, and to search for ferroelectric crystals possessing both high piezoelectricity and light transparency. The PI’s group has hosted numerous undergraduate students in the past for research training in computational materials research, including two recent NSF-REU students subsequently awarded NSF graduate fellowships. During the proposed project period, the PI’s group will continue to actively recruit both undergraduate students from its home institution and those from other institutions through the Penn State NSF-REU program(s) for research training as well as for mentoring training for the graduate students involved in the project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.